1. Field of the Invention
This invention relates to a mounting mechanism for a push rod of a master cylinder used in a hydraulic braking system or a hydraulic operating system of a clutch.
2. Description of the Related Art
A mechanism shown in FIG. 13 is known as a prior art mounting mechanism for a push rod of a master cylinder, for example, in Japanese Examined Utility Model Publication No. H03-15413.
FIG. 13 shows only a mounting mechanism for a push rod of a master cylinder. A cylinder hole 104 is formed in a cylinder main body 100, a piston 102 is slidably fitted into the cylinder hole 104, and a pressure chamber is defined between the piston 102 and the cylinder hole 104.
The piston 102 is pushed to left in FIG. 13 by a push rod 106. This push rod 106 has an end portion 105 held in contact with the piston 102 and is mounted in the cylinder main body 100. The push rod 106 is mounted into the cylinder main body 100 by inserting the end portion 105 into the cylinder hole 104, engaging a fastening member 107 for stopping a longitudinal movement with the end portion 105 and fixing the fastening member 107 by fitting a snap ring 108 into a groove 112 formed in the wall of the cylinder hole 104.
The end portion 105 is formed with a spherical projection 109, and the piston 102 and the push rod 106 are coupled by bringing the spherical projection 109 and a spherical recess 110 formed in the piston 102 together. The spherical projection 109 and the spherical recess 110 take the shapes of parts of spherical surfaces and the radii of curvature thereof are substantially equal.
The piston 102 is constantly pushed in a direction toward an opening 113 (rightward direction in FIG. 13) by a pushing force of a returning spring (not shown) for pushing the piston 102 or a hydraulic pressure by an operating device connected with the pressure chamber (e.g. a wheel cylinder of a braking system or a load acting on an operating cylinder of a hydraulic operating system of a clutch). Accordingly, the push rod 106 is stationary while being held in contact with the fastening member 107 in a non-operative state of an unillustrated pedal, whereas the push rod 106 is moved to left in FIG. 13 to be separated from the fastening member 107 when the pedal is operated, whereby the piston 102 is moved.
The spherical projection 109 of the end portion 105 and the spherical recess 110 of the piston 102 described above are designed to prevent a pushing position, where the push rod 106 pushes the piston 102, from being largely changed even if a pedal side (right side in FIG. 13) of the push rod 106 should shake.
In the prior art mounting mechanism thus constructed, the fastening member 107 for hindering a movement of the push rod 106 toward the opening 113 and the snap ring 108 for fixing the fastening member 107 are used at an opening end of the cylinder hole 104 as described above.
However, in this mechanism, it is necessary, upon mounting the push rod 106 into the end of the cylinder main body 100, to mount the fastening member 107 on the push rod 106, push the piston 102 by means of the end portion 105 of the push rod 106 to insert the fastening member 107 into the groove 112 and fit the snap ring 108 to fix the fastening member 107. Therefore, there is a disadvantage of necessitating a tool (ordinary tool, special tool or the like) for mounting the push rod 106 and a disadvantage of necessitating parts for mounting (ordinary fastening part, retaining part, etc.). Further, since the snap ring 108 and the fastening member 107 are small parts, an assembling operation is cumbersome.